Acetylcholine slows the heart rate and decreases blood pressure. The National Dysautonomia Research Foundation states that the most important transmitters in the autonomic nervous system are acetylcholine and norepinephrine.
Acetylcholine is a neurotransmitter, or a chemical that transmits signals throughout the brain and body. According to The Merk Manual, acetylcholine generally has inhibiting effects such as slowing the heart rate and decreasing blood pressure, but it also causes some sympathetic effects such as increased sweating or making hair stand on end. The National Dysautonomia Research Foundation emphasizes that acetylcholine is one of the chemicals that manage the transmissions between nerve endings and their corresponding organs.
While acetylcholine slows heart rate and blood pressure, another chemical messenger, norepinephrine, has the opposite effect. It can constrict blood vessels in order to naturally elevate blood pressure during such times as when you arise from sleeping. It also increases one's heart rate. Acetylcholine and norepinephrine can be seen as two sides of the same coin, as they are both chemical messengers used for communication within the body's autonomic nervous system, which is the part of the nervous system that controls the body's involuntary actions. These actions can include the beating of the heart and the widening and narrowing of blood vessels.